Reduce array of properties ReactiveSwift

Question

I have an array of Property<Int>, and I need to reduce them to get sum of the last inputs (it's basically an unread notification counter from different SDK's) and put that into new Property<Int>, I tried this

let unseen: Property<Int> = .init(
            initial: 0,
            then: countExtractor(counters: counters)
        )
     func countExtractor(counters: [Property<Int>]) -> SignalProducer<Int?, Never> {
    SignalProducer { observer, lifetime in
        guard !lifetime.hasEnded else {
            return
        }
        let producers = counters.map { $0.producer }
        lifetime += SignalProducer<SignalProducer<Int, Never>, Never>(producers)
            .flatten(.latest)
            .reduce(0) { previous, current in
                return (previous ?? 0) + current
            }
            .start(observer)
    }
}

And it's working, but the values are not updating (when I hard code only one property everything is working correctly)

Answer 1

The answer was so simple

 let properties = Property<Int>.combineLatest(counters)
let count = properties?.producer.map {
    $0.reduce(0, +)
}
guard let count = count else {
    return SignalProducer(value: 0)
}
return count

Answer 2

A bit simpler:

let sum: Property<Int> = Property
.combineLatest(counters, emptySentinel: [])
.map { $0.reduce(0, +) }